The present invention is related to wireless telecommunications equipment and, more specifically, to wireless telecommunications equipment, such as a telephone with two modes of operation (car and handheld), for use in a dual frequency band (Personal Communications Services and cellular frequencies).
With the proliferation of commercial wireless telecommunications services, it is only logical that a dual band wireless telephone is desirable by customers, and the user of the wireless telephone would like the flexibility of portable (handheld) operation for virtually limitless access to any calling party from any location. In addition, while in his or her car, for example, the user would like to connect this wireless telephone to the car antenna and operate it from the car battery in order not to utilize the nickel cadmium battery typically employed with cellular/PCS phones. This way, the telephone can be efficiently operated, while preventing a reduction in talk or standby time due to depleted charges of the nickel cadmium battery, for example.
Several problems, however, are generally encountered when switching between two antennas (car and handheld) in the dual-band operation. Any additional insertion loss, resulting from a series-connected switching device inserted for changing between the two operations, cannot be tolerated during the handheld operation. That is, if a closed switch exists in the series path between the antenna and the radio transceiver in the handheld operation, the insertion loss attributed to that switch increases the system noise figure, thereby decreasing the circuit sensitivity. Such a series inserted switch becomes prohibitive due to strict sensitivity requirements in the handheld operation.
In addition, the additional non-linearity from the series inserted switch could add to intermodulation and cross modulation problems (i.e., co-channel interference) in receiving applications. The switch could also cause spectral regrowth and increase adjacent channel power (i.e., adjacent channel interference) in transmitting applications. The non-linearity can be reduced by increasing a bias current to the switching device, but that would mean sacrificing the much needed talk and standby time due to additional power drawn from the handheld telephone battery.
The above problems are further exacerbated because the wireless phone is preferably operable in 2 frequency bands, namely PCS and cellular.
A need therefore exists for a system and method to overcome the above disadvantages.